Paul Walker's dad says Roger Rodas' family is holding $1.8 mil worth of his son's exotic car collection ... and he's demanding the cars or cash immediately.
Paul Walker III filed legal docs claiming the estate of Rodas -- who was driving the Porsche Carrera GT when he and Walker died -- is in possession of numerous vehicles belonging to his son.
In the docs, he says the cars were all fully or partially owned by Paul. Of course, Roger and Paul co-owned Always Evolving ... a performance and racing shop.
For what it's worth, Rodas' family already rejected the claim -- so it looks like a judge will have to sort this one out.